WorkShop Practice Lab Mannual

8/11/2019 WorkShop Practice Lab Mannual

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NUML- DEPARTMENT OF ENGINEERING ISLAMABAD

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A HAND BOOK

FOR

ELECTRICAL

WORKSHOP


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CONTENTS

Part 1 General1. Syllabus

2. Lab rules

3. Safety precautions

4. Electrical engineering - An overview

5. Electric power supply system

Part 2 Study of safety devices

1. Importance of safety devices

2. Circuit breakersMCB, MCCB & RCBO (ELCB) etc

3. Earthing systems

Part 3 House wiring

1. Introduction

2. Systems of distribution of electrical energy

3. Systems of wiring

4. Selection of wiring system

5.

Electrical wiring materials

Part 4 Experiments

1. One lamp controlled by one switch

2. Series connection

3. Parallel connection

4. Staircase wiring

5. Hospital wiring

6.

Go down wiring

7. Fluorescent lamp wiring

Part 5 Domestic appliances

1. Fan

2. Electric Mixer

3. Electric Iron

4. Refrigerator

5. Air conditioner6. Electric lamps


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Course Contents

List of study and practical exercises for Electrical Workshop:

Ex. No. 1: Study of power supplies and safety devices

Introduction to electrical supply system

Importance of Safety device in domestic installation

Study of safety devices such as Fuses, MCB, MCCB, ELCB

Earthing.Ex. No. 2: Electrical wiring practices (House wiring)

Distribution of electrical energy in a domestic electrical

installation

Study of wiring tools & accessories

Various types of domestic wiring

Exercise in wiring practice

One lamp controlled by one switch

Series and parallel connection

Staircase wiring Hospital wiring

Go down wiring

Plug socket connection

Fluorescent lamp wiring

Ex. No. 3: Study of domestic appliances

Study of different types of electric Lamps Incandescent lamp, Fluorescent, CFL, Metal

halide, Mercury vapour, Sodium vapour and halogen lamp.

Study of home appliancesMixie, Fan, Refrigerator, Air Conditioner, Iron box, Water heater

& Energy meter.

Ex. No. 4: PCB fabrication and soldering practice

Assembling and soldering of A stable multi-vibrator circuit on

a copper clad sheet.

Ex. No. 4:

Mini Project


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5.2 .5 Table Lamp Switch ...................................................................................... 41

5.2 .6 Bed Switch ................................................................................................. 41

5.3 Ceiling Rose ...................................................................................................... 42

5.4 Socket-Outlets .................................................................................................. 42

5.5 Plugs ................................................................................................................ 43

5.6 Lamp Holders .................................................................................................... 43

5.6.1 Batten Holders ............................................................................................. 43

5.6.2 Pendant or Cored Grip Holders ....................................................................... 44

5.6.3 Angle Holders .............................................................................................. 44

5.6.4 Slanting Holders ........................................................................................... 44

5.6.5 Bracket Holders ........................................................................................... 44

5.6.7 Water Tight Bracket Holder............................................................................ 44

5.6.8 Junction Box ................................................................................................ 44

5. Experiment: 4a Fan .............................................................................................. 45

5.1 Aim: - .............................................................................................................. 45

5.2 Construction ..................................................................................................... 45

5.3 SERVICING ....................................................................................................... 46

6. Experiment: 4b Electric food Mixer ...................................................................... 47

6.1 Aim:- ............................................................................................................... 47

6.2Working principle:- ............................................................................................. 47

7. Experiment: 4c ELECTRIC IRON BOX ........................................................................ 49

7.1Aim: - ............................................................................................................... 49

7.2 Working principle:- ............................................................................................ 49

7.3 Servicing .......................................................................................................... 50

8. Experiment 4d: Refrigerator .................................................................................. 508.1Introduction: ...................................................................................................... 50

8.2 The various components of a vapor compression refrigeration system are: ............... 50

8.3Compressor: ...................................................................................................... 51

8.4The basic mechanism of a refrigerator works like this:............................................. 52

8.5 Air Conditioner ..................................................................................................... 52

8.5.1 How Does an Air Conditioner Work? .................................................................. 52

8.6 Induction type single phase energy meter ............................................................... 54

8.7 Electric lamps....................................................................................................... 56


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8.7.1 Incandescent Lamps ........................................................................................ 56

8.7.2Tungsten Halogen Lamps .................................................................................. 57

8.7.3 Fluorescent Lamps .......................................................................................... 58

8.7.4Compact Fluorescent Lamps .............................................................................. 59

8.7.4a Mercury Vapour Lamps ................................................................................ 60

8.7.5Metal Halide Lamps .......................................................................................... 61

8.7.6 Sodium Vapour Lamps ..................................................................................... 62

Experiment No 5: TOOLS TO BE USED IN HOUSE WIRING .............................................. 65

10.1 HOUSE WIRING ............................................................................................... 67

10.1.1 Elements of House wiring: ........................................................................... 67

10.1.2 Wires and wire sizes: .................................................................................. 69

10.1.3 Fundamentals of Electricity: ......................................................................... 69

10.3.5.Safety Precautions :.................................................................................... 74

11. Experiment No: 6 ONE LAMP CONTROLLED BY ONE SPT SWITCH ............................... 76

11.1 Procedure: ...................................................................................................... 76

11.2VIVA QUESTIONS .............................................................................................. 77

12. EXPERIMENT NO: 7 AC Automatic Voltage Stabilizers and Regulators .......................... 78

12.1 A Design Technology Overview, Electronic Servo / Electro - Mechanical Design ........ 78

12.2 Design Advantages ........................................................................................... 79

12.3 Solid State Transductor / Saturable Reactor Design .............................................. 79

12.3.1 Design Advantages ..................................................................................... 80

12.4 Magnetic Induction Solid State Design ................................................................ 80

12.4.1Design Advantages ...................................................................................... 81

12.5 Ferro-Resonant - Super Isolation Solid State Design ............................................. 81

12.5.1 Design Advantages ..................................................................................... 8112.6 Electronic Tap Changing Solid State Design ......................................................... 82

12.6.1 Design Advantages ..................................................................................... 82

Design Disadvantages ........................................................................................... 82

13. EXPERIMENT NO 8: UNINTERRUPTIBLE POWER SUPPLY SYSTEM SELECTION,

INSTALLATION, AND MAINTENANCE FOR COMMAND, CONTROL, COMMUNICATIONS,

COMPUTER, INTELLIGENCE, SURVEILLANCE, AND RECONNAISSANCE FACILITIES ............. 83

13.1Principles and configurations .............................................................................. 83

13.1.1Static UPS. ................................................................................................. 83

13.1.2 Rotary UPS. ............................................................................................... 84


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13.2INSTALLATION AND TESTING OF UNINTERRUPTIBLE POWER SUPPLY (UPS) SYSTEMS

............................................................................................................................. 85

13.2.1Construction and installation of static UPS systems .......................................... 85

13.2.1a Construction features of static systems. There are several construction features

about the UPS that contribute to the system as a whole. ........................................... 85

13.3 Test equipment ................................................................................................ 88

13.3.1 UPS battery maintenance ............................................................................ 90

14. EXPERIMENT NO: 9 BATTERY ................................................................................. 93

Caution: ................................................................................................................. 93

14.1VISUAL INSPECTIONS ....................................................................................... 94

Monthly ............................................................................................................... 9414.2 BATTERY CARE ................................................................................................ 94

A. Adjustment of Specific Gravity ........................................................................... 94

B. Temperature .................................................................................................... 94

C. Cleanliness ...................................................................................................... 94

D. Spilled Electrolyte ............................................................................................. 94

14.3. CHARGERS ..................................................................................................... 94

A. Every Shift ....................................................................................................... 95

B. Quarterly ......................................................................................................... 95

C. Annually .......................................................................................................... 95

14.4 RECORDS ........................................................................................................ 95

14.5 BATTERY TROUBLES SUMMARIZED .................................................................... 96

14.5 RECOMMENDED ACTIONS ................................................................................. 97

14.6 LEAD-ACID BATTERY PRINCIPLES ...................................................................... 98

PURPOSE ............................................................................................................. 98

FULL CHARGE ...................................................................................................... 98

14.6.1CHEMICAL CHANGES ...................................................................................... 98

WELDING ................................................................................................................ 100

CARPENTRY ............................................................................................................. 109


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Experiment: 1 Introduction to Workshop Lab

1.1 General Workshop Rule

All students in the workshop are expected to adhere to the following guidelines. The students are supposedto come in proper workshop uniform dress. Wearing shoes in the workshop is compulsory.

Do not fool around in the lab: Take your lab work seriously and behave appropriately in the

laboratory. Be aware of your classmates safety as well as your own at all times. To successfully

complete the experiments in one lab period, you must come prepared to the laboratory. You must

read the experiment in advance and answer the pre-lab questions.

Please treat the instruments with care, as they are very expensive.

Return the components to the correct bins when you are finished with them. Before leaving the lab, place the stools under the lab bench.

Before leaving the lab, turn off the main power switch to the lab bench.

Keep your work area neat and uncluttered- Have only books and other materials that are needed to

conduct the experiment in the laboratory.

Experiment:The student works with a partner and they both take the data on separate notebooks.

The lab instructor will look at the data and sign on your notebook at the end of the experiment.

Any student missing a lab (not present in the lab) with no proper or reasonable excuse will get a 0

grade on that specific lab and will have his/her final letter grade reduced. Any student missing two

labs with no proper excuse will automatically get a failing grade (F).

This laboratory can be used by students during laboratory hours only.

1.2 Electrical Safety Principles:

When planning and performing work on electrical systems and equipment, keep these principles in mind:

Understand the procedure completely before starting the work.

Use good quality footwear/shoes in order to provide maximum resistance. Never energize any circuit unless you are sure that no one is working on the circuit. Give electric

supply to the wiring system only after thorough verification.

Before replacing a blown fuse always remember to put the switch off.

Do not touch switch boards, main switches, holder points etc with wet hands.

Do not use broken switches, sockets or plug.

Use non-conductive tools whenever possible.

Before putting the plug pins in socket put off the plug switch and disconnect the plug by pulling the

plug pin and not by pulling cable.


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2. Experiment: 2 Measurements of different electrical parameters

and safety devices

2.1 Some definitions:Electric current:Electric current can be termed as a continuous flow of electrons through a conductor. One

ampere is the current produced when a pressure of one volt is applied across a circuit having one ohm

resistance.

EMF: EMF is electro motive force. Potential difference between two points in a circuit is the electrical

pressure difference required to drive a current between them. Potential difference may be termed as voltage.

Voltage of a torch battery is 1.5 V and that of automobile battery is 12V. KSEB supply voltage for domestic

installation is 240 V.Electric power (watt):Electric power, P = Voltage * current * Power factor Unit of electric power is watt

(W)

Electric energy:Unit of electric energy is KWh (Kilo Watt hour) 1 unit energy = 1 KWh KSEB

provides one KWh meter at every Installation for measuring consumed energy. Resistance is the property of

a substance due to which it opposes the flow of current through it. Unit of resistance is ohm Resistance, R =

Specific resistance * I / A

Where I is the length of material & A is the area of cross section

Effect of temperature on resistance:-When temperature increases resistance of pure metals and Alloys

increases when temperature increases resistance of electrolyte, insulators etc decrease.

Resistance in series:-Consider three resistors connected in series, and then the total resistance of the circuit

will be the sum of the three resistors.

Ohms law:-Ohms law states that, the ratio of potential difference between any two points in a conductor to

the current flowing between them is constant. R = V /1 Keeping temperature constant.

Study of Electric Power Supply:

Eelectricity:Electricity is a form of energy. Electricity is the flow of electrons. We get electricity, which is

a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear

power, Hydel power and other natural sources, which are called primary sources.

Electric power supply system:

AC&DC:DC or direct current is steady current. It never changes its direction, and AC is alternating in

nature. AC voltage can be increased or decreased with the help of transformers. By using high voltage AC,

we can drastically reduce the transmission losses. AC can be converted into DC easily but reverse is not so

easy.


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In India state electricity boards are the authorities to generate and distribute electric energy. KSEB generates

electric power at a voltage of 11 KV. This power is transmitted by increasing the voltage at different levels

as 33 KV, 66KV, 110 KV, 220KVor 400 KV from different substations. At load centers this voltage again

stepped down as 11 KV and a feeder network is created. This feeder line energizes the 11KV/415V step

down transformer, and from these transformers electric supply can be given to consumers at 240V and 415

V as single phase or three phases.

All domestic and commercial consumers get electric energy from the distribution network of concerned

electricity boards. Based on the power requirements of consumers Electricity Boards may give 3-phase

connection (for high power) or single phase connection (for low power). In the three phase connections 4

wires are provided, where as in single-phase connection one phase and a neutral connection are provided to

the consumers. Phase to neutral voltage in our country is 230 V and phase-to-phase voltage is 400 V of

frequency 50 Hz. Most of the appliances work on single-phase supply. There are some motors, which

requires three phase supply.

A KWh meter is provided at the consumer end for measuring the electrical energy consumed.

KSEB introduces different tariffs for different consumers, as per their connected load and nature of

connection.

2.2 Study of safety devicesImportance of safety devices

The safety features are inbuilt with electric power distribution. The current is to flow through the path it is

expected to pass and should not take another path through which it is not expected to pass. Conductors made

of copper or aluminium are provided across the path for carrying the current and insulators like PVC, paper

or rubber are provided across the path through which the current is not expected to flow.

Under abnormal condition there can be failure of insulations and current will flow through the undesired

path which can cause damage to equipments and more important the safety of the user. Sometimes the user

may inadvertently touch a live conductor and cause electric shock. The circuit may also carry under short

circuit condition much more than normal value of the current. The inbuilt safety features will isolate the

faulty circuit from the rest of the supply.

The very high currents caused by short circuit situation can cause lots of damage to electrical installation.

Protective devices are needed to break short-circuit and overload currents.

Circuit breakers and fuses are protective devices that control the power going to a particular route of wiring.

In case of an overload or a short on that circuit, the breaker or fuse trips and automatically shuts off power to

that circuit. Fuses are the commonly used protection devices to protect components like wires, transformers


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electronics circuit modules against overload. The general idea of the fuse is that it "burns fuse link" when

current gets higher than it's rating and thus stops the current flowing.

2.3 Types of safety devices

Fuse

Circuit breakers( MCB, MCCB & ELCB)

Earthing

Basically two types of protections are provided in the power supply system of domestic consumers.

1. Protection from over current.

2. Protection from leakage current due to failure of insulation or inadvertent contact with live

conductors by the user.

Over current and Short circuit

One type of situation that wiring needs to be protected against is over current. The electrical wiring is rated

for certain maximum current. If you try to pull more current through it, the wiring will heat considerably.

When the wiring heats too much, it will cause the melting of cable insulation, cause fire if there is something

flammable near cable and even melt the copper conductors in the cable. So protection is needed to guarantee

that in case of something tries to pull too much current through mains wiring, this cannot happen for any

long time until the fuse blows and stops the current.

Many people are familiar with a "short circuit", which is a type of fault that occurs when two conductors of

an electric circuit touch each other. The current flow caused by a short circuit is usually high and rapid and

is quickly detected and halted by conventional circuit protective devices, such as fuses or circuit breakers.

Ground faults are one type of problem when the insulation fails.


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Human sensitivity to electricity

500mA Immediate cardiac arrest resulting in

Death.

70-100mA Cardiac fibillarillation; the heart begins

beats at a steady

20-30 mA Muscle contraction can cause respiratory

paralysis

10mA Muscle contraction : the person remains

stuck, to the conductor

1-10 mA Prickling sensations

However, electrocution should not be viewed in terms of current alone but in terms of contact voltage.

A person gets electrocuted by coming in contact with an object that has a different potential from

his/her own. The difference in potential causes the current to flow through the body.

The human body has known limits:

- Under normal dry conditions, voltage limit = 50V.

-In damp surroundings, voltage limit = 25V.

2.3.1 FUSES

Fuse is a wire of short length having low melting point which gives protection against excessive

current. This excessive current may be due to over load or short circuit. Under normal working

condition the current flowing through the circuit is within safe limit. But when some faults such as

short circuit occurs the current exceeds the safe limit value, the fuse wire gets heated and melts. This

will cause breaking of the circuit. After one fusing operation, fuse wire must be rewired with the

same size wire.

This basic guide will help you decide which fuse to fit to ensure the safe use of your householdappliances.


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Appliances up to 700 Watts = 3 Amp fuse

Appliances between 700 and 1000 Watts = 5 Amp fuse

Appliances over 1000 Watts = 13 Amp fuse

COMMON FUSE TYPES

1. Rewirable fuse

2. Cartridge fuse

3. HRC fuse

1. Rewirable fuse:

This is the cheapest method for protecting a circuit from short circuit. Wires of different diameters

made of lead and tin are used in the circuit. When large current flows these wires melts and

disconnects the faulty circuit from the rest of the supply.

There are different types of fuses. The usual type is the rewirable type in which the fuse wire is

carried in a removable fuse link (Fig. a). The fuse link is made of porcelain or other suitable

insulating material. The fuse carrier is push-fitted to the fuse base to make the connection through. An

advantage of this type is that the blown fuse wire can be replaced with negligible cost. But there is a

chance of selecting a wrong size of fuse wire. Another disadvantage with rewirable fuse is that it may

sometimes lead to fire hazards, when the fuse wire blows.

Fig. (a) Rewirable fuse

The semi enclosed rewirable fuses has the following drawbacks:

It normally melts on 50 % to 100 % excessive overload. The melting current cannot be

accurately predicted.

It takes time to rewire the fuse.

Standard fuse wire should be always made available.

However it is the cheapest mode of protection from short circuit.

2.Cartridge fuseCartridge fuse consists of a tube with metal end caps at both ends (Fig. b). The tube is usually made


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of glass with no filling material. The fuse wire is placed inside the tube, connected between the end

caps. Since the tube is made of glass, the fuse element can be easily inspected for breakage. When the

fuse is blown, the whole cartridge has to be replaced. The advantages of cartridge fuses are, quick and

easy replacement and the fuse rating is marked on the end cap of the cartridge itself. Cartridge fuses

are mainly: used in various electrical and electronic equipment.

3. High Rupturing Capacity Fuse (HRC):

This is a completely enclosed cartridge type of fuse. These fuses are screwed or linked in the circuit.

Generally it is used in the high power circuits. High Rupturing Capacity (HRC) fuse consists of a

porcelain tube! with metal end caps and fixing tags (Fig. c). The fuse element is held inside the tube

between the end caps and the tube is filled with silica sand or granulated quartz. When the fuseelement blows, the silica inside the tube prevent the formation of an arc, and thus avoids the

possibility of fire hazards. HRC fuse links are available in a range of 10A to 800A.

The HRC fuse has the following advantages:

It is very reliable.

It has an enclosed fuse wire, therefore no chance its arc doing any damage

to the surroundings.

It has low temperature rise at rated load.


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Fig. below shows the current path in a typical miniature circuit breaker when it is in the 'on' position.

The current passes through a solenoid coil and a bimetallic strip. When an overload condition persists

for a few seconds, the bimetallic strip bends and triggers the trip mechanism.

The principle of operation of an MCB is based on the following two principles.

a) Thermal operation

b) Magnetic operation

a) Thermal operation

In thermal operation, the extra heat produced by the high current warms the bimetal strip. This results

in bending the bimetallic strip and trips the operating contacts. The thermal operation is slow. Hence,

it is not suitable for speedy disconnection required to clear fault currents. However, it is ideal for

operation in the event of small but prolonged overload currents. Thus, in general the thermal

operation is suitable for opening the circuit in the event of excessive current due to the overloaded

machines.

b). Magnetic operation

The magnetic operation, on the other hand is suitable for protection against high short circuit currents.This magnetic operation is due to the magnetic field set up by a coil carrying the current, which


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attracts an iron part to trip the breaker when the

current becomes large enough. The magnetic operation is very fast and is used for braking fault

currents.

In most cases of MCB' s, both types are provided so that overload currents and short circuit currents

are handled with the same degree. It should however be remembered that the mechanical operation of

opening the contacts takes a definite minimum time, typically 20ms, so that there can never be the

possibility of truly instantaneous operation.

In many installations, MCBs are preferred over fuses mainly because there is no need of rewiring the

fuse wire or replacing the cartridge. MCBs are available in a range of 0.5A to 63A normal operating

current and for the entire range, the, physical dimensions are almost identical.

The major advantages of MCBs are

Instantaneous opening of the contact on short circuit faults

Can be designed to operate even for very small overload currents

They can be quickly reset by hand

They cannot be reclosed if fault persist

In many cases they preferred over fuses as there is no need to rewire it.

Earth Leakage Circuit Breaker

The earth leakage circuit breaker (ELCB) is a protective device, which will automatically trip, when there is

an earth leakage within the installation. It is also known as residual current circuit breaker (RCCB). It works

on the current balance principle. The main part is a core consisting of three windings. Here one winding

carries the phase current, the other winding carries the neutral current and the third winding to the tripping

circuit. Under normal operating conditions the net flux in the core is zero as such no emf induced in the trip

coil. However, when earth fault occurs, the phase and neutral current varies, the net flux in the core will be

different and as such, emf is induced in the trip coil and it is energized. It then opens the circuit. The

functioning of the ELCB can be checked using a switch.


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RCD- Residual Current Device. This is a generic term for the entire range of RCDs.

RCCB - Residual Current Circuit Breaker. This is basically a mechanical switch with an RCD

function added to it. Its sole function is to provide protection against earth fault currents.

RCBO- Residual Current Breaker with Over current Protection. This is basically an over current

circuit breaker (such as an MCB) with an RCD function added to it. It has two functions,

Types of RCD

RCDs can be divided into two categories based on the means by which they detect and respond to

earth fault currents. The two types are Voltage Independent (VI) and Voltage Dependent (VD). These

are sometimes also referred to as electromechanical and electronic types respectively. The VI type

uses the output energy from the CT to activate a relay which in turn activates a tripping mechanism

causing the RCD to trip. The VD type uses electronic circuitry to detect the earth fault current and to

activate a tripping mechanism causing the RCD to trip. The VI device derives its operating energy

from the earth fault current whereas the VD device derives its operating energy from the mains

supply.

2.3.3 Earthling

What is earthing /grounding?

Earthing or grounding is the term used for electrical connection to the general mass of earth.

Equipment or a system is said to be 'earthed' when it is effectively connected to the ground with a


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conducting object. Earthing provides protection to personal and equipment by ensuring operation of

the protective gear and isolation of faulty circuit during:

Insulation failure Accidental contact

Lightning strike

Importance of earthing

Earthing is necessary for proper functioning of certain equipments. Earthing is done also for

preventing the operating personal from hazardous shocks caused by the damage of the heating

appliances. Consider an electric heater connected to the supply using two-pin plug and socket. If by

some chance the heating element comes in contact with the metallic body of the heater, the body of

the heater being a conducting material will be at the same potential as the heating coil. If a person

comes and touches the body of the heater, current will flow through his body, which will result in an

electric shock.

To avoid unnecessary accident, it is recommended that electric heater be connected to a 3-pin socket

using a 3-core cable. (Note: To see a three-core cable, open a plug of an electric iron. There will be

three wires, red, blue and green. The green wire connected to the body of the iron is the earth wire) In

this case the body of the electric heater is connected to the green wire of the cable, which is connected

to the earth through the earth terminal. Besides the body of the electric heater, bodies of hot plates,

kettles, toasters, heaters, ovens, refrigerators, air conditioners, coolers, electric irons etc could be

earthed using three pin plugs. The resistance of the path to the earth terminal through the earth wire is

very low. Hence, even if the heating element comes in contact with the metallic body and a human

being comes in contact with the metallic body, major part of the current will flow only through the

earth wire (usually the green wire in a 3 core cable). Moreover because of the low resistance path, a

large current will flow through the phase wire and the fuse will blow off. For large current to flow,

earth resistance should be low. To achieve this proper earthing has to be done.

2.3.3a Earthing is classified as:

a. System earthing

b. Equipment earthing

System earthing:It is the earthing of neutrals of generating stations and substations. It is employed

to limit the voltage of live conductors with respect to potential of general mass of earth. This is

necessary to prevent failure of insulation.

Equipment earthing: Is earthing of non current carrying metal parts of electrical equipments. As per

Rules 33 and 61 of Indian Electricity Rule 1956 non-current carrying metal parts must be earthed with


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two separate and distinct earth continuity conductors to an efficient earth electrode. However

equipments with double insulation need not be earthed.

Some Definitions:Earthing: A tower/ equipments connecting to the general mass of earth by means of an electrical

conductor.

Earth Electrode:Connection to earth is achieved by electrically connecting a metal plate, rod or

other conductors or an array of conductors to the general mass of earth. This metal plate or rod or

conductor is called as "Earth electrode".

Earth lead: The conductor by which connection to earth is made.

Earth loop impedance:The total resistance of earth path including that of conductors, earth wire,

earth leads and earth electrodes at consumer end and substation end.

Factors affecting the value of earth electrode resistance

Electrode material.

Electrode size.

Material and size of earth wire.

Moisture content of soil.

Depth of electrode of underground.

Quantity of dust and charcoal in earth pit.

Earth resistance consists of following components

Resistance of metal electrode

Contact resistance between electrode and soil

Resistance of soil away from electrode surface.

The resistance decreases with the presence of moisture and salt in soil. To increase the effectiveness

of earth, the total earth resistance should be reduced. Efforts should be made to reduce the resistance

contributed by each of above three components.

Earth Electrodes

Earth electrodes can be following shapes

Driven Rods or pipes

Horizontal Wires

Four Pointed Stars

Conductive Plates

i)

Round Vertical Platesii) Square Vertical Plates


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Buried Radial Wires

Spheres made of metal

Water Pipes

Water pipe as earth electrode

As water pipes exist extensively and these are most of the time embedded in earth, they can make a

good earth electrode. Such earthing is not objectionable with alternating currents. But with direct

currents, the flow of fault currents in pipes produces electrolysis and results in heavy corrosion of

pipes. This electrolysis process makes the water also harmful to certain extent. If water pipes are

proposed to be used as earth electrode, then only main water supply pipe should be used as an

electrode. The water supply main pipe should have metal-to-metal joints between its segments. A

perfect electrical connection should be made between water pipe & earth conductor. Pipe should be

cleaned thoroughly with emery paper. Earth conductor also should be cleaned thoroughly. The

cleaned conductor should be wrapped 4 to 5 times and ends clamped by nuts & bolts. The earth

resistance achieved by such an arrangement is usually a fraction of an ohm. Low resistance of such

system is due to long length of water pipe and the fact that it is mostly embedded below earth. This

method is mostly used for grounding in telephone services. Electrodes should be made of a metal,

which has a high conductivity. Normally copper is used. The size of the electrode should be such, that

it is able to conduct the expected value of stray equipments. For example a 3 phase star wound

generator must have its neutral point at earth potential.

The salts commonly used for chemical treatment of soil are

Sodium Chloride

Calcium Chloride

Sodium Nitrate

Magnesium Sulphate

Other factors, which affect the soil resistivity, are

1. Temperature of soil: the resistivity increases when temperature falls below the freezing point. If

the temperature falls from 20degrees C to O degree C, soil resistivity goes up from 7200-ohm cm to

14000-ohm cm.

2. Moisture Content of Soil: Small changes in moisture content seriously affect the resistivity. For

example if the moisture content changes from 25% to 30%, soil resistivity drops from 250000-ohm

cms to 6400-ohm cm. It is important that earth electrodes should be in contact with moist soil. Itshould be ensured that the electrodes are deep in soil and if possible below the permanent water level.


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3. Mechanical Composition of soil: finer the grading, lower the resistance.

Methods of placing earth electrodes in soil

1. Pipe Earthing:

Fig. E (1) Cross section of pipe earthing

Pipe earthing is done by permanently placing a pipe in wet ground. The pipe can be made of steel,

galvanized iron or cast iron. Usually GI pipes having a length of 2.5m and an internal diameter of

38mm are used. The pipe should not be painted or coated with any non-conducting material.

Fig. E (1) shows an illustration of a typical pipe electrode. The pipe should be placed atleast 1.25m

below the ground level and it should be surrounded by alternate layers of charcoal and salt for a

distance of around 15 cm. This is to maintain the moisture level and to obtain lower earth resistance.

The earth lead of sufficient gauge should be firmly connected to the electrode and it should be carried

in a Gl pipe at a depth of 60cm below the ground level. A funnel with a wire mesh should be provided

to pour water into the sump. Three or four bucket of water should be poured in a few days particularly

during summer season. This is to keep the surroundings of the electrode permanently moist.


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2. Plate earthing

Fig. E (2) Plate earthing

A typical illustration of plate earthing is shown in Fig. E (2). The plate electrode should have a

minimum dimension of 600x600x3.15mm for copper plate or 600x600x6.3mm for Gl plates. The

plate electrode should be placed atleast 1.5m below the ground level. The earth conductor is to be

securely connected to the plate by means of bolts and nuts. The bolts and nuts should be of the same

material as that of the plate. The earth conductor should be carried in a Gl pipe buried 60 cm below

the ground level. The plate electrode should be surrounded by a layer of charcoal to reduce the earth

resistance. A separate Gl pipe with funnel and wire mesh attached is provided to pour water into the

sump.

3. Strip earthing

For all places having a rocky soil bed, this type of earthing is suitable. On this system, wires or strips

made of GI of size 25 mm x 4 mm or made of copper of size 25 mm x 1.6 mm are embedded 0.5 m,

below the soil in the form of a network. The length should not be less than 1.5 m as per ISI

specification. Details are given in figure below.


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Effect of Soil Properties in Earthing

While it is not possible to change the fundamental nature /properties of soil at a given location, but

local variations of soil conditions do occur even in a small area. When a location for making earthing

pit has to be selected, preference should be given to location, which is likely to give minimum

electrical resistance. In the list below, soils have been arranged in ascending order with regard to their

electrical resistance.

Wet marshy lands, or lands containing ashes (Avg Resistivity 2400 ohm cms)

Clay, loamy soil, arable land clay

Clay & loam mixed with varying proportion of gravel & sand (Avg Resistivity 15,800

ohm cms)

Damp & wet sands

Dry sand

Gravel & Stones

3. Experiment: 3: House Wiring

Introduction

A network of wires connecting various accessories for distribution of electrical energy from the

suppliers meter board to the numerous electrical energy consuming devices such as lamps, fans and

other domestic appliances through controlling and safety devices is known as wiring system.

The suppliers service cable feeding an installation terminates in what is usually called the service

fuses. In an ordinary house the service fuse is called as service cutout. Such cutouts including service

meters remain the property of the supplier and represent the furthest point of the supplier

responsibility. The point at which the consumer's wiring is connected into cutout is known as point

of commencement of supply or consumer's terminals. From consumer terminals onwards the supply

cables are entirely under the control of consumer's and so laid out as per his selection. A typical

house wiring circuit is shown in fig. a


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fig (a)

3.1 Systems of distribution of electrical energy

Since as per recommendations of ISI the maximum number of points of lights, fans and socket-outlet

that can be connected in one circuit is 10 and the maximum load that can be connected in such a

circuit is 800 watts, hence in case more load or more points are required to be connected to the

supply system, then it is to be done by having more than one circuit.

Distribution Board System


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In distribution board system, which is most commonly adopted for distribution of electrical energy in

a building, the fuses of various circuits are grouped together on a distribution board, some times

simply known as fuse board.

The two copper strips, known as bus-bars, fixed in a distribution board of hard wood or metal case are

connected to the supply main through a linked switch so that the installation can be switched off as a

whole from both the poles of supply if required. A fuse is inserted in the + ve or phase pole of each

circuit so that each circuit is connected up through its own particular fuse.

In large buildings, however, if only one distribution board were used, some of the points would be at

a considerable distance from it and in such cases it is advisable to employ sub-distribution boards

either to save cable or to prevent too great voltage drop at the more distant points (lamps or fans or

other appliances). In such cases main distribution board controls the circuit to each sub-distribution

board from which the sub-circuits are taken, as shown in fig. a

The number of circuits and sub-circuits are decided as per number of points to be wired and load to be

connected to the supply system. For determination of load of an installation the following ratings

maybe assumed unless the values are known or specified.

a) Fluorescent lamps40 watts.

b)

Incandescent lamps, fans, and socket outlets60 watts.

c) Power socket-outlets1,000 watts.

d) Exhaust fansas per capacity of exhaust fans.

The Tree System

Another system of distribution of electrical energy in a building is the tree system. In this system

smaller branches are taken from the main branch, as shown in fig. b and the wiring system resembles

a tree. As each branch is taken off, a fuse is inserted. This system used to be employed in early days.

Now-a-days it is no more adopted due to the following draw-backs in this system.

a) The voltage across all the lamps does not remain the same. The lamps in the last

branch will have least voltage across them on account of voltage drop in leads,

b) A number of joints are involved in each circuit.

c) Fuses are scattered.

d) In case of occurrence of fault all the joints have to be located and if some of these joints

are concealed beneath floors or roof spaces, a lot of difficulties are to be faced.

Sometimes a number of such joints are required to be opened for testing purposes, sodamage is caused to installation, conductors and building.


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3.2 Methods of wiring

There are two methods of wiring known as

a) joint box system (or Tee system) and

b) Loop-in system

1. Joint Box or Tee System:

In joint box system the connections to the lamps are made through joints made in joint boxes by

means of suitable connectors or joint cutouts. In this method though there is a saving in the quantity

of wire or cable required but the same is offset by the extra cost of joint boxes. The other

disadvantage of T-connections is that the number of T-connections made in a wiring system results

in weakness if not properly made. Now-a-days the use of this system is limited to temporary

installations only, as its cost is low.


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2. Loop- in- system:

This system is universally employed for connections of various lamps or other appliances in parallel.

In this system when a connection is required at a light or switch, the feed conductor is looped-in by

bringing it direct to the terminal and then carrying it forward again to the next point to be fed, as

shown in fig. d. The switch and light feeds are carried round the circuit in a series of loops from one

point to another until the last point on the circuit is reached.

The phase or line conductors are looped either in switch board or box and neutral conductors are

looped either in switch board or from light or fan. Line or phase should never be looped from light or

fan.

3.3 The advantages and disadvantages of loop-in system are as

follows;

Advantages

a) Joint boxes are not required.

b) In loop-in system no joint is concealed beneath floor or in roof spaces. As they are made only

at outlets so they are accessible for inspection and opening out merely by removing the

fitments concerned. Hence fault location is easy.

Disadvantages:

a) Length of wire or cable required is more and voltage drops and copper losses are,

therefore, more.

b) Looping-in switches and lamp holders is usually difficult.


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3.4 SYSTEMS OF WIRING

The types of internal wiring usually employed in our country are:

1. Cleat wiring:

In this system of internal wiring the cables used are either VIR or PVC type. The cables are held by

porcelain cleats about 6 mm above the walls or ceiling. The cleats are made in two halves, one base

and the other cap. The base is grooved to accommodate the cables and the cap is put over it and whole

of it is then screwed on wooden plugs (gutties) previously cemented into the wall or ceiling. Thus the

cables are firmly griped between the two halves of the cleats and secured to the supporting wall or

ceiling. The cleats used are of different sizes and different types in order to accommodate cables of

various sizes and different numbers of cables respectively. The cleats are of three typesone groove,

two grooves and three grooves to accommodate one, two, and three cables respectively.

Advantages:

a) It is the cheapest system of internal wiring.

b) Its installation and dismantlement is easy and quick.

c) Material is recoverable after dismantlement.

d)

Inspection, alterations and additions can be easily made.e) Skill required is little.

Disadvantages:

a) It is not good looking.

b) It is quite temporary and perishes quickly.

c) The wires are exposed to mechanical injury.

d) The insulation catches dampness from the atmosphere and common salt like substance appears

on the insulation which lowers the insulation resistance and Causes leakage. Hence this systemof wiring cannot be used in damp places.


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Advantages

a) Its installation is easy and quick and saving in labor largely compensate for the extra cost

of the cable.

b) Its life is long.

c) Within certain limits it is fire proof.

d) It can withstand the action of most chemicals such as acids and alkalies.

e) It is cheaper than other types of wiring except cleat wiring.

f) If the job is carried out with proper attention, it gives a nice appearance.

Disadvantages

a) Good workmanship is required to make a sound job in TRS wiring.

b) This type of wiring cannot be recommended for use in situations open to sun or rain

unless preventive steps are taken to preserve the insulation of cables.

Fields of Application

The TRS wiring is suitable for low voltage installations and is extensively used for lighting purposes

everywhere i.e. in domestic, commercial or industrial buildings except workshop where it is liable to

mechanical injury.

This type of wiring is suitable in situations where acids and alkalies are likely to be present.

4. Lead Sheathed Wiring

This type of wiring employs conductors insulated with VIR and is covered with an outer sheath of

lead aluminum alloy containing about 95% lead. This metal sheath gives protection to the cable from

mechanical injury, dampness and atmospheric corrosion. The whole lead covering is made electrically

continuous and is connected to earth at the point of entry to protect against electrolytic action due to

leaking current and to provide safety against the sheath becoming a live. The cables are run on

wooden batten and fixed by means of link clips as in TRS wiring. The great part of the cable

employed is flat twin (the cable having two insulated conductors side by side covered with red and

black tape respectively and under one flat covering of lead alloy). Three-core flat type cable is also

used in certain cases as well as single core cables under a circular sheath of lead alloy.

Advantages

a) It provides protection against mechanical injury better than provided by TRS wiring.

b) It is easy to fix and looks nice as it can be run in building without damaging

decoration and can be painted to suit colour scheme of the surroundings.

c)

Its life is long if proper earth continuity is maintained throughout.d) It can be used in damp situations provided protection against moisture effect on


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the ends of the cable is given.

e) It can be used in situations exposed to rain and sun provided no joint is exposed.

Disadvantagesa) It is costlier than TRS wiring.

b) It is not suitable for places where chemical corrosion may occur.

c) In case of damage to insulation the metal sheath becomes alive and gives shock, so as

to provide safety against electrical shock it is necessary that the sheath is properly

earthed and an earth wire is run side by side with it and all pieces are properly bounded

or joined together so that not a single cover is left unearthed.

d) Skilled labour and proper supervision is required.


This wiring system is suitable for low voltage (up to 250 volts) installations. It may be used in places

exposed to sun and rain provided no joint is exposed. It may also be used in damp places with a

suitable protective covering. It should not be used in places where chemical corrosion may occur..

This type of wiring is not very common in use these days except for some small installations and

distribution boards etc.

5. Conduit Wiring

In this system of wiring steel tubes, known as conduits, are installed on the surface of walls by means

of saddles or pipe hooks or buried under plaster and VIR or PVC cables are drawn into afterwards by

means of a GI wire of size of about 18 SWG. In damp situations the conduits can be spaced from the

walls by means of small wooden blocks fixed below the pipes at regular intervals. In order to

facilitate drawing of wires numbers of inspection fittings are provided along its length. The conduits

should be electrically and mechanically continuous and connected to earth at some suitable point. The

conduits used for this purpose are of two types namely (i) light gauge (or split type) conduit and

heavy gauge (or screwed type) conduit. Light gauge or split conduit with a seam along its length is

used for cheap work. It is not water tight or even damp proof and is not permitted on medium voltage

(i.e. on voltages higher than 250V). Screwed conduit (solid drawn or with welded seam) is used for

all medium voltage (250 V or 600 V) circuits and in places where good mechanical protection and

absolute protection from moisture is desired. In general the finish of the conduit is black stove-

enamelled, there being a smooth coating of enamel both on the inside and outside surface of the tube.

Galvanized conduit is also employed, especially in damp situation when the conduit is on the surface

but under ordinary conditions buried in walls it offers little, if any, advantage over good enamelledconduits.


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Advantages

a) It provides protection against mechanical damage.

b) It provides complete protection against fire due to short-circuits etc.

c) The whole system is water proof.

d) Replacement and alteration of defective wiring is easy.

e) Its life is long if the work is properly executed.

f) It is shock proof also if earthing and bonding is properly done.

Disadvantages

a) It is very costly system of wiring.

b) Its erection is not so easy and requires time.

c) Experienced and highly skilled labour is required for carrying out the job.

Internal condensation of moisture may cause damage to the insulation unless the system outlets are

properly drained and ventilated


As this system of wiring provides protection against fire, mechanical damage and dampness

so this is the only approved system of wiring for:

a) Places where considerable dust or puff is present such as in textile mills, saw mills, flour

mills etc.

b) Damp situations.

c) In workshops for lighting and motor wiring.

d) Places, where there is a possibility of fire hazards such as in oil mills, varnish factories etc.

e) Places, where important documents are kept such as a record room.

f) Residential and public buildings, where the appearance is the prime thing. The recessed type

conduit wiring is preferred for residential and public buildings.

3.6 CHOICE OF WIRING

The following factors should be considered before selecting a particular type of wiring.

a. Safety: The first and foremost consideration is safety to a person using electricity against

leakage or shock. Where there is a possibility of fire hazard, conduit wiring is used.

b. Mechanical Protection: The wiring must be protected from mechanical damage during use.

c. Permanency:The wiring must not deteriorate unduly by action of weather, fumes, dampness

etc.

d.

Appearance:The wiring should he good looking.

e. Durability: The wiring must be durable.


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f. Accessibility: In wiring system there should be facilities for extension, renewal or alterations.

g. Initial Cost:The wiring selected should suit the pocket of the owner of the building.

h. Maintenance Cost:The wiring should have, as far as possible, the lowest maintenance cost.

The other factors, in addition to above, to be kept in view while making the choice of wiring is load

voltage to be employed, type of building etc.


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4.Tools to be in Electric Wiring


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5. STUDY OF WIRING ACCESSORIES

Any device,associated with the wiring and electrical appliance of an installation, such as a switch, a

fuse, a plug, a socket-outlet etc. is called the wiring accessory. The cables, flexible cords and variouswiring accessories in common use are briefly described below

5.1 Cables:

The cable or wire used in internal wiring is covered with insulation. The conductor is covered with

insulation so that it may prevent leakage of current from the conductor and thus minimize the risk of

fire and shock.

The wire employed for internal wiring of buildings may be divided into different groups according to

a.

Conductor usedb. number of cores used

c. voltage grading and

d. type of insulation used

According to the conductor material used in cables, these may be divided into two classes known as

copper cables and aluminum cables.

According to the number of cores, the cable consists of, the cables maybe divided into the classes

known as single core cables; twin core cables; three core cables; two core with ECC (earth

continuity conductor) cables etc.

According to voltage grading the cables may be divided into two classes:

(i) 250/440 volt cables

(ii)650/1,100 volt cables.

According to type of insulation the cables are of the following types:

5.1.1 Vulcanized Indian Rubber (VIR) Cables:

VIR cables are available in 250/440 volt as well as in 650/ 1100 volt grades and are used for general

electrical wiring in cleat, casing-capping and conduit wirings.

VIR cable consists of either tinned copper conductor or aluminum conductor covered with a layer of

vulcanized Indian rubber insulation. Over the rubber insulation cotton tape sheathed covering is

provided with moisture resistant compound bitumen wax or some other insulating material for

making the cables moisture proof. The thickness of rubber insulation depends upon the voltage grade

for which the cable is required.

The copper conductor is tinned to provide protection against corrosion due to presence of traces of

sulphr, zinc oxide and other mineral ingredients in the VIR.


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5.1.2 Tough Rubber Sheathed (TRS) or Cab Type Sheathed (CTS)

Cables:

These cables are available in 250/440 volt grades and used in CTS'(or TRS) wiring. TRS cable isnothing but a vulcanized rubber insulated conductor with an outer protective covering of tough

rubber. These cables are water proof, hence can be used in wet conditions. These cables are available

as single core, circular twin core, circular three core, flat three cores, twin core with an earth

continuity conductor etc. In wiring of a three pin plug separate earth wire may be used, as it will be

cheaper in cost and easy in installation.

These cables are cheaper in cost and lighter in weight than lead alloy sheathed cables, described

later and have the properties similar to those, of lead sheathed cables.

5.1.3 Lead Sheathed Cables:These cables are also available in 250/440 volt grades and are used for internal wiring where climatic

condition is not dry and has a little bit moisture. The lead sheathed cable is a vulcanized rubber

insulated conductor covered with a continuous sheath of lead. The lead sheath provides very good

protection against the absorption of moisture and sufficient protection against mechanical injury and

so can be used without casing or conduit system. It is available as a single core, twin core, flat three

core and flat twin core with an earth continuity conductor.

5.1.4 Polyvinyl Chloride (PVC) Insulated Cables:

These cables are available in 250/440 and 650/1,100 volt grades and are used in concealed wiring

system. In this type of cable conductor is insulated with PVC insulation. Since PVC is harder thanrubber so PVC cable does not require cotton tapping and braiding over it for mechanical and moisture

protection.

Since the PVC is thermo-plastic insulation, so it is affected at high temperatures and it may soften and

flow down. These cables cannot be used for giving connections to the heating appliances, pendant

lighting etc. Though the insulation resistance of PVC is lower than that of VIR but its effect is

negligible for low and medium voltages below 600 volts,

5.1.5Weather Proof/Cables

These cables are used for outdoor wiring and for power supply or industrial supply. These cables are

either PVC insulated or vulcanized rubber insulated conductors being suitably taped (only in case ofvulcanized rubber insulated cable) braided and then compounded with weather resisting material.

These cables are available in 250/440 volt and 650/1100 volt grades. These cables are not affected by

heat or sun or rain.

Although TRS cables can be used for outdoor purposes but due to their higher cost, weather proof

cables are generally used for outdoor services.

5.1.6 Flexible Cords

A cable containing one or more cores, each formed of a group of wires, the diameter of cores and of

the wires being very small to afford flexibility, is known as flexible cord. These are used as

connecting wires for such purposes as from ceiling rose to lamp holder, or from socket-outlet to

portable apparatus such as radios, fans, lamps, heaters etc. The flexibility of such wires facilitate in


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handling the appliances and prevent the wires from breakage. The flexible cords used for house hold

appliances are available in various pleasing colours, sizes and of various thickness of insulation.

These wires should never be used for fixed wiring.

Switches

A manually operated device used for closing and opening or for changing the connections of a circuit

is known as a switch.

The switches used in internal wiring may be classified in various ways. According to the type of base

material they are classified as porcelain or bakelite switches. According to colour of base they are

either white or black or brown coloured switches. According to operation required, they are classified

as one way, two-way, centre off, double pole etc. switches.

5.2 One-way Switch

This type of switch consists of two terminals which can be easily seen from the back side of theswitch as well, without removing the cover. The switch is always connect* din series with the point

(lamp, fan or socket-outlet) to be controlled.

5.2 .1Two-way Switch

The switch of this type consists of four terminals, two of them being short-circuited inside the switch.

The switch of this type is usually used for the stair-case wiring or circuits where one point is to be

controlled from two different places.

5.2.2 Two-way Centre off Switch

The switch of this type is just like a two-way switch but having three operations. In the centre it

becomes off. Such switches are used when two lamps are to be operated alternately.

5.2 .3 Double Pole Switch

This is a combination of two one-way switches, which can be operated simultaneously as ON-OFF

terminals of both the switches, are connected together by a handle made of bakelite. Such switches are

used as interlinked switches when the load current is less than 5A and supply voltage is

under250V.Incaseeither of the voltage or current exceeds the limits mentioned above DPI C switch is

used.

5.2 .4 Push-button Switches

Such switches are used for controlling the electric bells. When the knob is pressed, the circuit iscompleted and the bell rings and as soon as the knob is left, the circuit becomes open.

5.2 .5 Table Lamp Switch

This is a small on-off switch which is commonly used in table lamps.

5.2 .6 Bed Switch

Such switches are used to switch off the table lamps or other lamps while going to sleep or making

the lamp on while getting up at night. It is connected in aeries with one of the two flexible wires. The

specialty with this switch is that fluorescent material is applied to its knob so that it may glow at night

and can easily be seen in darkness. This is a pendant type switch.

The switches are of two types known as surface switches (or tumbler switches) and flush switches (or


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concealed switches).

5.2.6a Tumbler or Surface Switches

Tumbler switches are those which are fixed on the mounting blocks directly fixed on the surface of

the wall. Such switches project out the surface of the wall and are in common use. Surface switches

are available in round and oblong base. Round base switches are cheap and in common use. Oblong

surface switches are good in appearance, but being costly, are rarely used.

5.2.6b Flush Switches

Flush switches, as obvious from their name, are fixed in flush with the wall and do not

project out. These switches are used where high quality performance and appearance are

required.

5.3 Ceiling Rose

The ceiling rose is used to connect the pendant lamps, fans or fluorescent tubes to the installation

through flexible or silk covered wires. These are not used on a circuit, the voltage of which

normally exceeds 250 volts.

Fig26.8 shows a modern form of molded ceiling rose which includes the earth terminal and a

shrouded terminal for looping in live wire.

5.4 Socket-Outlets

The socket-outlets are used to supply electrical connections whenever required for electrical

appliances such as radios, table fans, table lamps, iron, stoves etc. Socket-outlets are of two types

two pin type and three pin type. Two pin socket-outlets have become obsolete now-a-days. The three

pin type socket-outlet has got three hollow terminals in which three pin plugs can easily be inserted

but not loosely. Two holes being of same size, are meant for making connections to the flexible wire

of the appliance and the third hole, which is bigger comparatively, is meant for earth connections.

Thus three holes or sleeves are for live, neutral and earth connections. The three pin socket-outlets arealso of two types:

(i) 5 A for table fans, table lamps, radios etc, and

(ii)15 A for power circuits as heater, stove, iron etc.


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5.6.2 Pendant or Cored Grip Holders

Such a lamp holder is used when the lamp is to be suspended from the flexible cord. Such a lamp

holder is hanged vertically downward from the ceiling with flu flexible cord, one end of which makes

electrical connections with the ceiling rose and other with the lamp holder and thus with the lamp.

Pendant Lamp Holder

5.6.3 Angle Holders

Such lamp holders are used when the lamps are to be fixed directly on the walls and to give light at

an angle. Such lamp holders are available in various fancy designs and colors.

5.6.4 Slanting Holders

Such lamp holders are used for lamps to be fixed on advertising boards, for flood lights and for stage

lights. Such lamp holders are used along with shades (hand shape shades) so that light is concentrated

on the material displayed and does not trouble the viewer.

5.6.5 Bracket Holders

Such lamp holders are used to give direct light in the room or above a particular place. These cannot

be fixed on the roof or made to hang. Usually these are fixed on the wall. These may also be used in

table lamps.

5.6.7 Water Tight Bracket Holder

Such lamp holders are provided with tubular glasses fixed with water tight cover. Such lamp holders

are used outside the houses and for street lighting where there is no cover to save the bulb from

falling of water over it.

5.6.8 Junction BoxIn joint box system of wiring all joints in conductors are made by means of suitable connectors or


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joint cutouts in junction boxes. In looping back system of wiring, which is widely used now-a-days,

junction boxes are not required.

Domestic appliances

Some of the commonly used domestic appliances are Fan Food mixer Iron box Refrigerator Air Conditioner

5.Experiment: 4a Fan

5.1 Aim: -

To study the working and maintenance of table fan ceiling fan

Theory:-

Fan is an essential home appliance nowadays and is available in different style and facili-ties.

Generally used types are table fan and ceiling fan. We can mount the ceiling fan on the ceiling for

providing wind to whole the room. As per IE rule the minimum height from floor to fan must be2.5

meter? Table fan can be places on tabletop or any flat surface. But it has minimum space limit

compared to ceiling fan.

5.2 ConstructionMain parts of a ceiling fan are

(a)Winding(b)Capacitor &(c)RegulatorWinding of the motor can be done manually or by automated machine. Regulator may be electronic

type or resistance type. Electronic type regulator has negligible power loss and compact size. But in

the case of resistance type, resistances are connected in series with the circuit; this may cause power

loss as heat.

In table fan one permanent split capacitor run (PSC) motor is the heart of a fan. This motor consists of

two windings one as starting winding and other as running winding. Starting winding of this motorhas high resistance and low reactance but running winding has low resistance and high reactance. One

capacitor is connected in series with the starting winding and whole of this circuit is put in parallel

across running winding. In the case of ceiling fan these two windings are placed in stator in the inner

side of the fan. Rotor has no winding; it is the outer body of the fan. Ceiling fan motor operates just in

opposite manner as compared to general motor. That is actual rotor of the motor is blocked and the

stator is free to rotate. So ceiling fan runs in anticlockwise direction. At

the same time table fan motor is operated as normal case and so it runs in clockwise direction.

Capacitor connected in series with the starting winding should be value 2.5 micro farad. Pyranel

insulated foil paper capacitor is using for this purpose. It helps to provide a split phase effect fromsingle phase AC supply.


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5.3 SERVICINGProblems and solutions normally occurring in fans are as follows

1.Fan is not working when supply is given Check the supply at the consuming end. Dismantle the fan from ceiling and remove the cover. Check the windings,

if it is burnt rewind it with proper gauge copper wire. Number of turns must be equal to the previous winding, because it may affect the speed of

the fan. If starting winding is burnt, it alone can be replaced but in the case of runningwinding we want change these two sets of windings.

2.Fan is not starting and will work when push to start Check the voltage at the consuming end Dismantle the capacitor from fan and connect it to AC supply for 30 sec. Then disconnect

and short circuit the capacitor terminals. At that time we can hear one spot sound if itworking, otherwise it can be replaced by new one.

Check the bearing of the motor; if it is dirty grease may be applied


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6. Experiment: 4b Electric food Mixer

6.1 Aim:-

To study the principle of working and servicing of mixer (Mixy)

6.2Working principle:-

Mixer is an essential home appliance used for dry grinding, wet grinding mixing and other purposes.Different types of blades are used for these purposes. These blades can be replaced for specific workon the same shaft itself. The power rating of the mixer is varies from 500W to 600W according tovarious manufacturers. The speed of this motor is around 1800 rpm. The motor used in mixer isuniversal type. So it can be operated on AC and DC. In this type motor stator winding and rotorwinding are connected in series through two carbon brushes which is in contact with the segments ofthe commutator. One over load relay is put in series with this circuit for providing overload

protection. Generally used relay has current rating of 2 A. This relay get tripped when the loadbecome more than the specified. When mixer become off while using (due to tripping of relay) wecan reset it by pressing the button provided at the bottom of the mixer. One speed controlling knob is

provided for controlling the speed of the motor. This can be done by adjusting the number of fieldwinding tappings.Universal motors

The Universal motor is the most common type of high speed motor found in appliances and portable

line operated power tools. Typical uses include vacuum cleaners, floor polishers, electric drills,

routers, and sewing machines. They are likely to be found anywhere medium power, high speed,

and/or variable speed controls are required capabilities.

Construction consists of a stationary set of coils and magnetic core called the 'stator' and a rotating

set of coils and magnetic core called the 'armature'. Incorporated on the armature is a rotating switch

called a commutator?Connection to the armature is via carbon (or metal) contacts called 'brushes'

which are mounted on the frame of the motor and press against the commutator. Technically, these

are actually series wound DC motors but through the use of steel laminated magnetic core material,

will run on AC or DC - thus the name universal.

Changing direction requires interchanging the two connections between the stator and the armature.

This type of motor is found in blenders, food mixers, vacuum cleaners, sewing machines, and many

portable power tools.

Speed control of DC motors:The speed of a dc motor is given by the relation

N Eb/

When Eb = V-IaRa

N V-IaRa/

From the above equation it is clear that the speed of Dc motors can be controlled;

By varying flux per pole. This is known as flux or field control method.

By varying the armature drop, i.e. by varying the resistance of the armature

circuit. This is known as armature control method.


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By varying the applied voltage. This is known as voltage control method.

Field control method: The speed of series motor can be controlled by varying the fluxproduced by the series field winding. The variation flux can be brought about by tapping

the field winding.

Tapped field control:

In food Mixers tapped field control method is used for varying the speed. In this method

the number of turns of the series field winding can be changed by short circuiting a part

of it as shown in figure.

We know that the flux produced by the winding depends upon the ampere turns (i.e. Ise x No. of

turns). As the number of turns is reduced, the speed of the motor increased (N 1/ ).

Servicing

1. Mixer produces spark and smoke

Check wires and connections

Check the brushes and replace it, if it gets damaged. We can by the same

brushes from the market for replacing

2. Mixer is not working.

Check the cable and winding

Check the overload relay. Replace it if it gets damaged. This over load relay can be

buying from market.3. Jar of the mixer becomes loose.

Dismantle the coupler shaft and check the washer.If it gets damaged replace or add

two or three washers.,


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cause to stop the flow of current through heating element. While ironing when temperature reduces

than pre fixed value bimetal strip regains its normal position and the circuit again com-pleted. An

indicator lamp of 3.8 V is connected in the circuit on the handle of iron box to indicate the working.

Automatic iron boxes are now available in light weight form with power rating 750 W.

7.3 Servicing1. Iron box is not working

Check the supply at consuming end

Check the thermostat for open circuit

Check the heating element continuity

2. Iron box has no enough temperature when knob is placed at one position.

Check the heating element.

Adjust the screw below the knob to produce enough temperature.3.

Shock on body

Check the continuity of earth wire to body. If it does not get continuity dismantle the

cover and connect earth wire properly.

8.Experiment 4d: Refrigerator

8.1Introduction:

Refrigeration systems are used for maintaining low temperature say from 20 degree Celsius down to

very low temperature, as those required for food prseveration, industrial applications, laboratories etc.

The Purpose of Refrigeration:The fundamental reason for having a refrigerator is to keep food cold.Cold temperatures help food to stay fresh longer. The basic idea behind refrigeration is to slow down

the activity of bacteria (which all food contains) so that it takes longer for the bacteria to spoil the

food.

Refrigeration: It is the process of removing heat at a low temperature level and rejecting it at a

relatively higher temperature level. By its nature heat flows from a body at a higher temperature to

another at a lower temperature.

Refrigeration is accomplished by various methods such as vapour compression system, absorption

system, steam jet refrigeration cycle. The vapour compression cycle is used in most house hold

refrigerators.

Refrigerant: Refrigerants are heat carrying medium, which during their cycle in the refrigeration

system absorb heat at a low temperature level and discard the heat so absorbed at a higher level.

8.2 The various components of a vapor compression refrigeration

system are:

Evaporator Refrigerant Compressor

Condenser and Throttling device(capillary tube) Thermostat Fan


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8.4The basic mechanism of a refrigerator works like this:

The compressor compresses the refrigerant gas. This raises the refrigerant's pressure andtemperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerantto dissipate the heat of pressurization.

As it cools, the refrigerant condenses into liquid form and flows through the expansion valve. When it flows through the expansion valve, the liquid refrigerant is Allowed to move from a

high-pressure zone to a low-pressure zone, so it expands and evaporates. In evaporating, itabsorbs heat, making it cold.

The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside ofthe refrigerator cold. The cycle then repeats.

8.5 Air Conditioner

An air conditioner removes heat and moisture from the air by passing it over a cold surface. When

warm, moist "inside" air is blown across the surface of the unit's cooling coil, the air temperature

drops and the water vapor in it condenses making the air cooler and drier and therefore more

"comfortable."

Room air conditions are installed on windows or wall openings. The assembly incorporates a

refrigeration unit, and double shaft fan motor with fans mounted on both sides of the motor, one on

the evaporator side and other for the air cooled condenser. The room (or cooling) side and the outdoor

(or heat rejection) side of the unit are separated by an insulated patrician within the casing.

8.5.1 How Does an Air Conditioner Work?

Air conditioners and refrigerators work the same way. Instead of cooling just the small, insulated

space inside of a refrigerator, an air conditioner cools a room, a whole house, or an entire business.Air conditioners use chemicals that easily convert from a gas to a liquid and back again. This

chemical is used to transfer heat from the air inside of a home to the outside air.


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8.6 Induction type single phase energy meterInduction type instruments are used only for a.c measurements. Th

WorkShop Practice Lab Mannual

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